#!/usr/bin/env python
# -*- coding:utf-8 -*-
__author__ = 'shawn'

from collections import defaultdict

d = defaultdict(list)
d['a'].append(1)
d['a'].append(2)
d['a'].append(3)

print(d)

d = defaultdict(set)
d['a'].add(1)
d['a'].add(2)
d['b'].add(4)
print(d)

